The present invention relates to integrated circuit packaging, and particularly to packaging of integrated circuits which are capable of RF transmission or reception.
As integrated circuit technology advances, the maximum frequency imposed by the technology is continually increasing. Even without the use of III-V technology, ordinary silicon technology can routinely achieve switching times of well under ten nanoseconds in simple CMOS configurations. By using differential circuitry, and/or biasing which increases the level of static power consumption, higher frequencies of operation can be achieved. Using bipolar process technology, high frequency unity-gain cutoff limits far above 1 GHz can easily be achieved. Some published results have reported unity-gain frequencies (f.sub.T) in excess of 10 GHz with silicon technology.
Wireless communications requires an antenna to transmit and receive signals in the form of electromagnetic radiation. The antenna is driven by a discrete device or an integrated circuit. This "driver" chip is typically located in a package on a PC board along with other electronic circuitry. The signal from the driver chip reaches the antenna through a wire or cable.
Integrated Circuits with Wireless RF Interface
Many applications are attractive for RF interfaces from integrated circuits, particularly for low power RF interfaces. Traditional examples of such applications are keyless-entry automobile security systems, secure identification badges, antitheft devices, etc. Also, a sufficiently cheap and reliable micropower RF technology could replace the infrared LEDs which are currently used to provide a remote control capability in many consumer devices. More recently localized RF data communications between computing devices have become an area of considerable interest. Another area of interest is localized wireless voice communications, e.g. in cordless telephones and baby monitors. Another area of interest (and a very large market indeed) is cellular telephones (including the newer mobile communications services just being opened up in the United States).
In such applications, a small antenna is typically designed into the module to provide the RF coupling.
Background: Antenna Technology
Antenna technology is one of the most important branches of RF technology. At the same time, it poses unique analytical challenges, since RF problems often require detailed solutions of Maxwell's Equations with numerous constraints to achieve the needed near-field analysis. A vast amount of literature has been published in this area; see e.g. the HANDBOOK OF ANTENNAS (1st ed. Jasik 1961; 2nd ed. Johnson and Jasik; 3rd ed. 1994), all of which are hereby incorporated by reference. Good introductory reference material may be found in the various editions of the ARRL's ANTENNA HANDBOOK and VHF HANDBOOK, all of which are hereby incorporated by reference.
In general, as frequencies are increased, the typical size of an antenna element can be reduced for a given degree of directionality. Directionality can be increased by making the antenna physically larger.
Microwave Packaging Technology
At microwave frequencies (3 GHz and above), waveguides are frequently used for signal routing (since many dielectric materials are lossy at microwave frequencies, and since waveguides totally avoid radiation losses). To launch a signal into a waveguide (or extract a signal from the waveguide), a very simple inductive or capacitive probe is normally sufficient. For coupling to the RF signal in the waveguide, solid-state microwave devices have therefore sometimes been positioned inside the waveguide.
Innovative Compact Antenna Technology
The present invention takes integration one level higher. In the present invention, a metallic RF antenna is used as part of the integrated circuit package. This approach provides additional compactness, and exploits the high frequency capabilities of contemporary integrated circuits.
In this invention, the antenna serves as the package for the semiconductor driver chip. The requirement for a separate package to house the driver chip as well as for the wire or cable between the driver chip and the antenna are eliminated. When the back surface of the driver chip is an active terminal of the driver chip, the need for a separate load to that region may also be eliminated.
The antenna can also serve as a heat sink to dissipate power generated in the driver chip. If the driver chip is enclosed by the antenna, unwanted electromagnetic radiation can also be reduced or eliminated.
One class of embodiments uses the antenna both for RF coupling and also as a heat sink for the integrated circuit. This provides a synergy between two requirements of coupling integrated circuits to the outside world which had heretofore been considered separately.
This invention is particularly advantageous at VHF and UHF frequencies. At lower frequencies, it is more difficult to get a reasonable electrical cross-section in an antenna of reasonable size, whereas at higher frequencies it is more difficult to avoid strong (and sometimes unpredictable) directional patterns.